ABSTRACT
Numerous physiological changes occur at fertilization that profoundly affect the activity of the egg, e.g. changes in permeability to small molecules, oxygen uptake, carbohydrate metabolism and synthesis of DNA, RNA and protein. The mechanism of transport activation may require both early and late events of egg activation, involving increased energy metabolism. Nuclear transplantation experiments showed that brain cell nuclei injected into mature amphibian eggs undergo DNA synthesis which is replicative rather than repair. When DNA synthesis begins before pronuclear fusion, it occurs simultaneously in both pronuclei. A modification found on the 3' polyadenylation of mRNA with codycepin has no apparent effect on the rise of protein synthesis or polysome formation. Hence, it appears that the rate of protein synthesis in eggs and zygotes is primarily controlled by availability of mRNA. The level of glycolytic intermediates and hexose phosphate is low in the eggs of some sea urchins, which may limit the oxidative breakdown of carbohydrates and respiration.
